Toxicity of Halifax Harbour Sediments: an Evaluation of the Microtox® Solid-Phase Test

Abstract

Abstract Subtidal sediments were collected in Halifax Harbour, Nova Scotia, in July and August, 1992, to study sediment toxicity and hazards near the proposed location of a sewage treatment plant and outfall. A set of 110 samples from eight stations was evaluated. Interstitial water from surface (0-2 cm) and subsurface (2-4 cm) sediments was analyzed by the Microtox® 100% toxicity test protocol. The sediment particles were analyzed using the Microtox® solid-phase test. Interstitial water from surface and subsurface sediments from all stations was usually non-toxic, compared to a phenol standard. The mean 5 min-EC50 of surface sediments (n=57) was 5,433mg/L; the mean 5 min-EC50 of subsurface sediments (n=50) was 804 mg/L. Toxicity thresholds for the harbour sediments were compared with National Research Council marine analytical sediment reference materials and a selection of natural sediments, and ranked. An experiment with the marine reference sediments (certified for PAHs and trace metals) and their mixtures showed the ability of the solid-phase test to discriminate among different levels of contaminated sediments. Intra- and inter-sample variability in toxicity at different locations in relation to time, sediment depth, sediment properties, and types and concentrations of contaminants was evaluated by multivariate and PCA tech-niques. This laboratory-field study provided insights into the sensitivity, repro-ducibility, significance and discriminatory ability of the Microtox® solid-phase bioassay and its value in the study of complex natural sediment mixtures.